How do I make car acceleration in my game?
I'm not very sure if this is how you will like it, but I have a different idea. As you press W, the car's property 'accelerate' will increase. If the property is from interval 0-40; the property will have +6 added every time you hit W (with frequency: 10); the same applies for 41-80; 81-120; etc. It will add less in lower interval, and higher as it goes. For more realism, you can make a lot of intervals where it will add less to the 'accelerate' property when it is at a high speed. Now, when you hold W, the property will add as it looks like acceleration. All that is left is to bind it with however you have done your motion, such as "the car goes x fast if interval is from z to y," just play around with the values. You can do a very similar technique for deceleration. I have a GIF that is uploading right now of the logic bricks. I will add it to this answer ASAP.

GIF: http://recordit.co/Ahw2QIeaLu
-The intervals in the gif are very ruggid, they are: 0-40, 41-80, 81-120. For a racing game, you would want it much smoother, so you may have to do by tens or even five so it can be perfected. When you open the webpage for gif, just pay attention to debug properties.